No abstract

Duplex stainless steels (DSS) have a microstructure consisting of 50% ferrite α and 50% austenite γ. This two-phase microstructure provides the duplex stainless steels with attractive mechanical and corrosion properties. However, the microstructure is very dependent on the heat treatment and chemical composition. During the welding process, the temperature reached in the heat-affected zone (HAZ) retransforms austenite into ferrite. Due to the high cooling rates, only a part of the ferrite is retransformed into austenite. This tends to modify the 50/50 phase equilibrium. The cooling rate is linked not only to heat input but also to the thickness of the welded plates. Most of the standards limit the ferrite content in the range from 30 to 70%. However, the 70% limit for ferrite content in HAZ may be difficult to obtain especially for heavy plate thicknesses. To limit the maximum ferrite content in HAZ, a duplex stainless grade with high nitrogen and nickel within the 2205 composition range, called Arctic 2205, was developed. This paper will provide details on ferrite content measurement by metallographic method and welding results obtained on industrial welds showing very low and stable ferrite content in HAZ. Mechanical properties obtained on these welds at low temperature will also be reported, pushing the limits of use of duplex from − 50 °C (− 58 °F) down to − 100 °C (− 148 °F).

International audienceThe sensitivity of precipitation-strengthened A286 austenitic stainless steel to stress corrosion cracking was studied by means of slow-strain-rate tests. First, alloy cold working by low cycle fatigue (LCF) was investigated. Fatigue tests under plastic strain control were performed at different strain levels (Δεp/2 = 0.2%, 0.5%, 0.8% and 2%) to establish correlations between stress softening and the deformation microstructure resulting from the LCF tests. Deformed microstructures were identified through TEM investigations. The interaction between oxidation and localized deformation bands was also studied and it resulted that localized deformation bands are not preferential oxide growth channels. The pre-cycling of the alloy did not modify its oxidation behaviour. However, intergranular oxidation in the subsurface under the oxide layer formed after exposure to PWR primary water was shown